Magnetoresistive smart switch

ABSTRACT

A smart switch has a magnetic operator, at least one magnetic sensor located to sense movement of the magnetic operator, and a processor that processes an output of the magnetic sensor so as to detect right and left over travel ranges and a normal operating range of the magnetic operator. The magnetic sensor may be a magnetoresistive sensor.

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a highly reliable switch thathas no contact with a moving object and that is capable of detecting itsown failure and/or over travel range.

BACKGROUND OF THE INVENTION

[0002] Switches are used in a variety of applications to control the onand off states of loads, to sense the proximity or position of inputdevices, to provide inputs to data processing systems, and so on. Manyof these applications involve complex systems, such as those used onaircraft or oil wells, which rely on a large number of switches. Many ofthese switches experience intensive use in these systems and, as aresult, fail because their parts simply wear out. Switches can also failbecause they are driven or otherwise travel out of range.

[0003] Many of the switches used in complex systems provide criticalfunctions. When a switch that provides a critical function fails, thefailure can result in a potentially dangerous and/or economically costlycondition. Therefore, when such a switch fails, it is important toreplace it as soon as possible in order to avoid or minimize thepotentially dangerous and/or economically costly condition. However,when a switch fails in a complex system, it can be very difficult tolocate it so that it can be replaced.

[0004] The switch of the present invention is a non-contact positionsensor with a built in self-diagnostic system. The self diagnosticsystem can indicate that the switch travel out of range and/or that theswitch is not functioning properly. This switch has less wear because itdoes not contact the object that it is sensing, and there is less chancethat this switch will travel out of range. Therefore, the switch of thepresent invention has a longer life. Also, this switch detects when ithas failed so that it can be easily located and replaced.

SUMMARY OF THE INVENTION

[0005] In accordance with one aspect of the present invention, a smartswitch comprises a magnetic operator, at least one magnetic sensorlocated to sense movement of the magnetic operator, and a processorarranged to process an output of the magnetic sensor so as to detect anover travel range and a normal operating range of the magnetic operator.

[0006] In accordance with another aspect of the present invention, asmart switch comprises a magnetic operator, first, second, and thirdmagnetoresistive sensors located to sense movement of the magneticoperator, and a processor arranged to process outputs of the first,second, and third magnetoresistive sensors so as to detect right andleft over travel ranges and a normal operating range of the magneticoperator.

[0007] In accordance with still another aspect of the present invention,a smart switch comprises a magnetic operator, a single magnetoresistivesensor located to sense movement of the magnetic operator, and aprocessor arranged to process an output of the single magnetoresistivesensor so as to detect an over travel range and a normal operating rangeof the magnetic operator.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] These and other features and advantages will become more apparentfrom a detailed consideration of the invention when taken in conjunctionwith the drawings in which:

[0009]FIGS. 1 and 2 illustrate a smart switch according to oneembodiment of the present invention;

[0010]FIG. 3 illustrates the voltage versus position outputs of theindividual magnetoresistive sensors that are included in the smartswitch of FIGS. 1 and 2;

[0011]FIG. 4 illustrates an analog apparatus for processing the outputsshown in FIG. 3;

[0012]FIG. 5 illustrates a waveform produced by the analog apparatus ofFIG. 4;

[0013]FIG. 6 illustrates the detection ranges of the waveform shown inFIG. 5;

[0014]FIG. 7 illustrates a digital apparatus for processing the outputsshown in FIG. 3;

[0015]FIGS. 8 and 9 illustrate a smart switch according to anotherembodiment of the present invention;

[0016]FIG. 10 illustrates an apparatus for processing the output of thesmart switch shown in FIGS. 8 and 9; and,

[0017]FIG. 11 illustrates the detection ranges provided by the smartswitch of FIGS. 8 and 9.

DETAILED DESCRIPTION

[0018] As shown in FIGS. 1 and 2, a switch 10 according to oneembodiment of the present invention includes three magnetoresistivesensors 12, 14, and 16 mounted on a mounting surface 18. Themagnetoresistive sensor 14 is located between the magnetoresistivesensors 12 and 16, and the magnetoresistive sensors 12 and 16 arepositioned on either side of the magnetoresistive sensor 14. Themagnetoresistive sensors 12, 14, and 16 sense the position of a switchoperator 20, such as an actuator, a door, an oscillating shaft, etc., asthe switch operator 20 moves over the magnetoresistive sensors 12, 14,and 16 in the direction shown by the double ended arrow of FIG. 2.

[0019] As the switch operator 20 passes over it, each of themagnetoresistive sensors 12, 14, and 16 is mounted on the mountingsurface 18 so as to produce a corresponding one of the voltage outputs22, 24, and 26 shown in FIG. 3. Accordingly, the magnetoresistive sensor12 produces the voltage output 22, the magnetoresistive sensor 14produces the voltage output 24, and the magnetoresistive sensor 16produces the voltage output 26.

[0020] For example, each of the magnetoresistive sensors 12, 14, and 16may be a HMC1501 or HMC1512 supplied by Honeywell International, themagnetoresistive sensors 12 and 14 may be separated on the mountingsurface 18 by a distance of 2-40 mm, and the magnetoresistive sensors 14and 16 may be separated on the mounting surface 18 by the same distance.Also, the switch operator 20, for example, may be a magnet or othermagnetic field generating device. Given these devices and distances, themagnetoresistive sensors 12, 14, and 16 produce the voltage outputs 22,24, and 26 relative to the travel of the switch operator 20 along themounting surface 18 from one end to another.

[0021] As shown in FIG. 4, the voltage output 22 from themagnetoresistive sensor 12 is supplied to a comparator 30, the voltageoutput 24 from the magnetoresistive sensor 14 is supplied to anamplifier 32, and the voltage output 26 from the magnetoresistive sensor16 is supplied to a comparator 34. The outputs of the comparator 30, theamplifier 32, and the comparator 34 are added by a logical gate 36 toproduce the waveform 38 shown in FIG. 5. FIG. 5 shows the output of thelogical gate 36 as a function of travel of the switch operator 20 overthe limited range offered by the magnetoresistive sensors 12, 14, and16.

[0022] The comparator 30 has a threshold set so that it switches on whenthe voltage output 22 is below a first threshold, such as 0.05 volt, soas to provide an output at a level 40 of the waveform 38. The signalfrom the amplifier 32 at this point is comparatively smaller than apredetermined value so that the logical gate 36 passes the level 40 andnone of the outputs from the amplifier 32 and the comparator 34.

[0023] As the voltage output 22 rises sufficiently, the comparator 30switches off at a point 42. Because the comparator 34 is still off atthis point, only the output of the amplifier passes through the logicalgate 36. Accordingly, only the amplified voltage output 24 contributesto the output of the logical gate 36. The output of the logical gate 36during the time that both the comparator 30 and the comparator 34 areoff is the portion 44 of the waveform 44.

[0024] The comparator 34 has a threshold set so that it switches on whenthe voltage output 26 is sufficiently large so as to provide an outputat a level 46 of the waveform 38. The signal from the amplifier 32 atthis point 48 is now comparatively smaller than the level 46 so that thelogical gate 36 passes the level 46 and none of the output from theamplifier 32 and the comparator 30. Accordingly, the output of thelogical gate 36 holds at the level 46.

[0025]FIG. 6 illustrates that the waveform 38 may be broken into a leftover travel range to indicate that the switch operator 20 has traveledtoo far to the left, a right over travel range to indicate that theswitch operator 20 has traveled too far to the right, a normal operatingrange between the left over travel range and the right over travelrange. Also, one or more points in the normal operating range of theoutput shown in FIG. 7 can be used to indicate position of the switchoperator 20. For example, these points can be used to determine whetheran actuator is in one or more predetermined positions, whether a door isopen or shut, whether an oscillating shaft has traveled to one or morepredefined positions, etc.

[0026]FIG. 4 illustrates an analog approach to processing the voltageoutputs 22, 24, and 26. Alternatively, FIG. 7 illustrates a digitalapproach to processing the voltage outputs 22, 24, and 26. The voltageoutput 22 from the magnetoresistive sensor 12, the voltage output 24from the magnetoresistive sensor 14, and the voltage output 26 from themagnetoresistive sensor 16 are multiplexed by a multiplexer 60. Theoutput from the multiplexer 60 is amplified by an amplifier 62 andconverted to a digital signal by an analog-to-digital converter 64. Thedigital signal from the analog-to-digital converter 64 is then processedby a microprocessor 66 to produce the waveform 38 shown in FIG. 5.

[0027] Additionally, when the output from the switch 10 below apredetermine threshold is detected, or when the outputs from the threemagnetoresistive sensors 12, 14, and 16 do not follow the expectedpattern, it can be determined that the magnet or other magnetic fieldgenerating device of the switch operator 20 has fallen off of theactuator, or that the switch operator 20 has otherwise malfunctioned, orthat the switch 10 has become disconnected from its processing circuitsuch as shown in FIG. 4 or 7.

[0028] As shown in FIGS. 8 and 9, a switch 80 according to anotherembodiment of the present invention includes a single magnetoresistivesensor 82 mounted on a mounting surface 84. The magnetoresistive sensor82 is used to sense the position of a switch operator 86. As shown inFIG. 10, a processor 88 may be used to shape the output of themagnetoresistive sensor 82 so that this output has the generalappearance of the curve of FIG. 11. The processor 88 may bemicroprocessor based as shown in FIG. 7, or have two comparators, anamplifier, and logical gate as shown in FIG. 4, or other devicesarranged to profile the output of the magnetoresistive sensor 82according to the shape shown in FIG. 11.

[0029] As shown in FIG. 11, the output of the magnetoresistive sensor 82can be used to determine whether the switch operator 86 has traveled toofar to the right or left. Also, one or more points in the normal rangeof the output of the magnetoresistive sensor 82 can be used to indicateposition of the switch operator 86. For example, these points can beused to determine whether an actuator is in one or more predeterminedpositions, whether a door is open or shut, whether an oscillating shafthas traveled to one or more predefined positions, etc.

[0030] Additionally, by detecting that the output from themagnetoresistive sensor 82 is below a predetermine threshold, or whenthe output from the magnetoresistive sensor 82 does not follow theexpected pattern, the processor 88 can determine that the magnet orother magnetic field generating device has fallen off of the switchoperator 86, or that the switch operator 86 has otherwise malfunctioned,or that the switch 80 has become disconnected from the processor 88.

[0031] The embodiment illustrated in FIGS. 8-11 has the advantage ofsimplicity and lower cost. However, the overall range (voltage versusposition) from the left over travel range through the normal operatingrange to the right over travel range is shorter than the overall rangeof the embodiment illustrated in FIGS. 1-7.

[0032] Certain modifications of the present invention have beendescribed above. Other modifications of the present invention will occurto those practicing in the art of the present invention. For example,instead of using the microprocessor 66 to process the signal shown inFIG. 7, other processors such as ASICs may be used to process thevoltage outputs 22, 24, and 26. Similarly, an ASIC or other device orlogic array may comprise the processor 8.

[0033] Moreover, the outputs of the magnetoresistive sensors 12, 14, and16 may be processed by apparatus other than that specifically describedabove in order to process the voltage outputs 22, 24, and 26 and todetect over travel, magnet loss, or other failures of the switch 10.

[0034] Also, it is also possible to use more than three sensors in orderto extend the travel range. In this case, the outputs from the middlesensors can be combined and the processor can be used to determine theposition.

[0035] Furthermore, the processing arrangements shown in FIGS. 4 and 7may be high temperature processing arrangement to improve reliability.

[0036] In addition, the switch 10 is described above as includingmagnetic sensors in the form of the magnetoresistive sensors 12, 14, and16. Instead, these magnetic sensors may be other types of magneticsensors such as anisotropic magnetoresistive sensors, giantmagnetoresistive sensors, Hall sensors, etc. Similarly, themagnetoresistive sensor 82 may be an anisotropic magnetoresistivesensor, a giant magnetoresistive sensor, a Hall sensor, etc.

[0037] Moreover, temperature compensation may be provided for theswitches described above. For example, the microprocessor 66 may store anumber of temperature coefficients that are accessed depending on thetemperature of the switch as sensed by a temperature sensor 90 shown inFIG. 7 coupled to the multiplexer 60. Accordingly, one of thetemperature coefficients corresponding to the temperature sensed by thetemperature sensor 90 is accessed by the microprocessor 66 and is usedby the microprocessor 66 to characterize the output of themagnetoresistive sensors 12, 14, and 16. In this manner, the effect oftemperature on the outputs of the magnetoresistive sensors 12, 14, and16 may be minimized. Temperature compensation may similarly be appliedin the case of the circuit shown in FIG. 10.

[0038] Accordingly, the description of the present invention is to beconstrued as illustrative only and is for the purpose of teaching thoseskilled in the art the best mode of carrying out the invention. Thedetails may be varied substantially without departing from the spirit ofthe invention, and the exclusive use of all modifications which arewithin the scope of the appended claims is reserved.

We claim:
 1. A smart switch comprising: a magnetic operator; at least one magnetic sensor located to sense movement of the magnetic operator; and, a processor arranged to process an output of the magnetic sensor so as to detect an over travel range and a normal operating range of the magnetic operator.
 2. The smart switch of claim 1 wherein the at least one magnetic sensor comprises at least one magnetoresistive sensor.
 3. The smart switch of claim 1 wherein the at least one magnetic sensor comprises first, second, and third magnetic sensors located so as to sense movement of the magnetic operator, and wherein the processor is arranged to process respective outputs of the first, second, and third magnetic sensors so as to detect a right over travel range of the magnetic operator, a left over travel range of the magnetic operator, and a normal operating range of the magnetic operator.
 4. The smart switch of claim 3 wherein the first, second, and third magnetic sensors comprise corresponding first, second, and third magnetoresistive sensors.
 5. The smart switch of claim 3 wherein the processor comprises an analog processor.
 6. The smart switch of claim 5 wherein the processor is arranged to process the combined output so that the combined output has a substantially flat left over travel voltage versus position range, a substantially flat right over travel voltage versus position range, and a sloped normal operating voltage versus position range between the substantially flat left over travel voltage versus position range and the substantially flat right over travel voltage versus position range.
 7. The smart switch of claim 5 wherein the analog processor comprises: a first comparator coupled to the first magnetic sensor; an amplifier coupled to the second magnetic sensor; a second comparator coupled to the third magnetic sensor; and, a logical gate coupled to the amplifier and the first and second comparators.
 8. The smart switch of claim 7 wherein the processor is arranged to process the combined output so that the combined output has a substantially flat left over travel voltage versus position range, a substantially flat right over travel voltage versus position range, and a sloped normal operating voltage versus position range between the substantially flat left over travel voltage versus position range and the substantially flat right over travel voltage versus position range.
 9. The smart switch of claim 3 wherein the processor comprises a digital processor.
 10. The smart switch of claim 9 wherein the processor is arranged to process the combined output so that the combined output has a substantially flat left over travel voltage versus position range, a substantially flat right over travel voltage versus position range, and a sloped normal operating voltage versus position range between the substantially flat left over travel voltage versus position range and the substantially flat right over travel voltage versus position range.
 11. The smart switch of claim 9 wherein the digital processor comprises a microprocessor.
 12. The smart switch of claim 11 wherein the processor is arranged to process the combined output so that the combined output has a substantially flat left over travel voltage versus position range, a substantially flat right over travel voltage versus position range, and a sloped normal operating voltage versus position range between the substantially flat left over travel voltage versus position range and the substantially flat right over travel voltage versus position range.
 13. The smart switch of claim 1 wherein the processor comprises an analog processor.
 14. The smart switch of claim 13 wherein the processor is arranged to process the combined output so that the combined output has a substantially flat left over travel voltage versus position range, a substantially flat right over travel voltage versus position range, and a sloped normal operating voltage versus position range between the substantially flat left over travel voltage versus position range and the substantially flat right over travel voltage versus position range.
 15. The smart switch of claim 13 wherein the analog processor comprises: a first comparator coupled to the magnetic sensor; an amplifier coupled to the magnetic sensor; a second comparator coupled to the magnetic sensor; and, a logical gate coupled to the amplifier and the first and second comparators.
 16. The smart switch of claim 15 wherein the processor is arranged to process the combined output so that the combined output has a substantially flat left over travel voltage versus position range, a substantially flat right over travel voltage versus position range, and a sloped normal operating voltage versus position range between the substantially flat left over travel voltage versus position range and the substantially flat right over travel voltage versus position range.
 17. The smart switch of claim 1 wherein the processor comprises a digital processor.
 18. The smart switch of claim 17 wherein the processor is arranged to process the combined output so that the combined output has a substantially flat left over travel voltage versus position range, a substantially flat right over travel voltage versus position range, and a sloped normal operating voltage versus position range between the substantially flat left over travel voltage versus position range and the substantially flat right over travel voltage versus position range.
 19. The smart switch of claim 17 wherein the digital processor comprises a microprocessor.
 20. The smart switch of claim 19 wherein the processor is arranged to process the combined output so that the combined output has a substantially flat left over travel voltage versus position range, a substantially flat right over travel voltage versus position range, and a sloped normal operating voltage versus position range between the substantially flat left over travel voltage versus position range and the substantially flat right over travel voltage versus position range.
 21. The smart switch of claim 1 wherein the processor is arranged to process the combined output so that the combined output has a substantially flat left over travel voltage versus position range, a substantially flat right over travel voltage versus position range, and a sloped normal operating voltage versus position range between the substantially flat left over travel voltage versus position range and the substantially flat right over travel voltage versus position range.
 22. The smart switch of claim 1 wherein the processor comprises an ASIC.
 23. The smart switch of claim 1 wherein the processor is arranged to process the output of the magnetic sensor so as to detect a right over travel range of the magnetic operator, a left over travel range of the magnetic operator, and a normal operating range of the magnetic operator.
 24. The smart switch of claim 1 wherein the processor is arranged to perform self-diagnostics on the smart switch.
 25. The smart switch of claim 24 wherein the self-diagnostics include determining that a failure has occurred when the processor detects that the output from the magnetic sensor is below a predetermined threshold.
 26. The smart switch of claim 24 wherein the self-diagnostics include determining that a failure has occurred when an output from the magnetic sensor is not in accord with a predetermined pattern.
 27. The smart switch of claim 24 wherein the processor comprises high temperature electronics.
 28. The smart switch of claim 1 wherein the processor is arranged to provide temperature compensation to an output of the magnetic sensor.
 29. A smart switch comprising: a magnetic operator; first, second, and third magnetoresistive sensors located to sense movement of the magnetic operator; and, a processor arranged to process outputs of the first, second, and third magnetoresistive sensors so as to detect right and left over travel ranges and a normal operating range of the magnetic operator.
 30. The smart switch of claim 29 wherein the processor is arranged to process the combined output so that the combined output has a substantially flat left over travel voltage versus position range, a substantially flat right over travel voltage versus position range, and a sloped normal operating voltage versus position range between the substantially flat left over travel voltage versus position range and the substantially flat right over travel voltage versus position range.
 31. The smart switch of claim 29 wherein the processor comprises a microprocessor.
 32. The smart switch of claim 29 wherein the processor comprises an ASIC.
 33. The smart switch of claim 29 wherein the processor is arranged to determine a failure when the processor detects that the output from at least one of the first, second, and third magnetoresistive sensors is below a predetermined threshold.
 34. The smart switch of claim 29 wherein the processor comprises: a first comparator coupled to the first magnetoresistive sensor; an amplifier coupled to the second magnetoresistive sensor; a second comparator coupled to the third magnetoresistive sensor; and, a logical gate coupled to the amplifier and the first and second comparators.
 35. The smart switch of claim 29 wherein the processor is arranged to provide temperature compensation to an output of the first, second, and third magnetoresistive sensors.
 36. A smart switch comprising: a magnetic operator; a single magnetoresistive sensor located to sense movement of the magnetic operator; and, a processor arranged to process an output of the single magnetoresistive sensor so as to detect an over travel range and a normal operating range of the magnetic operator.
 37. The smart switch of claim 36 wherein the processor is arranged to process the output of the single magnetoresistive sensor so as to detect a right over travel range of the magnetic operator, a left over travel range of the magnetic operator, and a normal operating range of the magnetic operator.
 38. The smart switch of claim 36 wherein the processor is arranged to process the output of the single magnetoresistive sensor so that the output has a substantially flat left over travel voltage versus position range, a substantially flat right over travel voltage versus position range, and a sloped normal operating voltage versus position range between the substantially flat left over travel voltage versus position range and the substantially flat right over travel voltage versus position range.
 39. The smart switch of claim 36 wherein the processor comprises first and second comparators to produce the substantially flat left over travel voltage versus position range and the substantially flat right over travel voltage versus position range.
 40. The smart switch of claim 36 wherein the processor is arranged to determine a failure when the processor detects that the output from the single magnetoresistive sensor is below a predetermined threshold.
 41. The smart switch of claim 36 wherein the processor comprises a microprocessor.
 42. The smart switch of claim 36 wherein the processor comprises an ASIC.
 43. The smart switch of claim 36 wherein the processor is arranged to provide temperature compensation to an output of the single magnetoresistive sensor. 